FUSE observations of molecular hydrogen on the line of sight towards HD 141569A

¹ Laboratoire d'Astrophysique de Marseille, CNRS-Université de Provence, BP 8, 13376 Marseille Cedex 12, France e-mail: Claire.Martin@oamp.fr
² Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA
³ Carnegie Institution of Washington, Washington, DC, USA
⁴ Department of Physics and Astronomy, JHU, Baltimore, MD, USA
⁵ Institut d'Astrophysique de Paris, France

Received: 17 December 2004
Accepted: 12 May 2005

Abstract

We present an analysis of the Far Ultraviolet Spectroscopic Explorer (FUSE) spectrum of HD 141569A, a transitional object known to possess a circumstellar disk. We observe two components of gas at widely different temperatures along the line of sight. We detect cold H₂, which is thermalized up to at a kinetic temperature of ~51 K. Such low temperatures are typical of the diffuse interstellar medium. Since the line of sight to HD 141569A does not pass through its disk, it appears that we are observing the cold H₂ in a low extinction envelope associated with the high Galactic latitude dark cloud complex L134N, which is in the same direction and at nearly the same distance as HD 141569A. The column densities of the higher J-levels of H₂ suggest the presence of warm gas along the line of sight. The excitation conditions do not seem to be consistent with what is generally observed in diffuse interstellar clouds. The observed radial velocity of the gas implies that the UV spectral lines we observe are likely interstellar in origin rather than circumstellar, although our absorption line study does not definitely rule out the possibility that the warm gas is close to the star. The discovery of such warm gas along the line of sight may provide evidence for turbulent phenomena in the dark cloud L134N.